Termination and joint for tap-proof cable

ABSTRACT

Our invention relates to cable terminations and joints and particularly to terminations and joints for tap-proof communication cables.

United States Patent Inventors Erich W. Kothe White Plains; Andrew C. Laird, Hastingsmu-Hudson, both of N.Y.

Appl. No. 335,518

Filed Jan. 3, 1964 Patented Oct. 19, 197] Assignee Anaconda Wire and Cable Company TERMINATION AND JOINT FOR TAP-PROOF CABLE 1 1 Claims, 5 Drawing Figs.

U.S. Cl. 174/19, 174/21 R, 174/22 R Int. Cl. ..H02g 15/22,

50 FieldofSearch 174/19, 20, 21, 21.3, 22,222, 85, 74, 75.2, 88.2, 128

[ 5 6] References Cited UNITED STATES PATENTS 2,016,004 10/1935 Gay 174/21x 2,179,971 11/1939 Wentz 174/22 Primary Examiner-Richard A. Farley Attorney- Victor F. Volk ABSTRACT: Our invention relates to cable terminations and joints and particularly to terminations and joints for tap-proof communication cables.

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' SHEET 10F 3 Fig -M T I I I I I I I I I I II7"I7I/I I INVENTORS ERICH W.KOTHE ANDREW c. LAIRD PATENTEDum 19 l97l 3,614,289 SHEETZUF 3 PATENTEDnm 19 mt SHEET 30F 3 ERICH w. KOTHE BY ANDREW C,LAIRD TERMINATION AND JOINT FOR TAP-PROOF CABLE In a copending application, Ser. No. 226,286, by one of theinventors in the present invention there is described a communication cable-rendered tapproof by means of three concentric shields surrounding the core of communication conductors. The shields are insulated from each other by corona-free dielectric layers. The inside and outside shields are grounded and the center shield is energized at a voltage high enough to initiate a corona discharge between the shields if any voids are created in one of the dielectric layersJenetration through the shields to the cable core for the purpose of introducing a tapping probe could not be accomplished without introducing some void or disturbing the dielectric and any.attempt to tap the cable is instantly detected by a sensitive ionization detector that forms'an element of thecable installation. The signal being. transmitted is then instantly discontinued as a consequence of the alarm signal generated by the detector.

Terminations and joints in the tapproof cable cannot be made byknown cable splicing means because of the need to keep such terminations and joints free from any corona discharges that would be picked up by the sensitive ionization detector.

We have, however, invented a termination for the abovedescribed tapproof cable which will remain free from corona discharges. y

We have also invented jointing means for the tapproof cable which will not only be free from corona discharge but will, itself, be tap-proof.

Our termination and joint is for a tapproof cable comprised of a plurality of conductors forming a core, a first conducting wall surrounding the core and a first layer of insulation surrounding the wall in corona-freecontact therewith. A second conducting wall surrounds this layer in corona-free contact and a second layer of insulation surrounds the second conducting wall, also in corona-free contact. In corona-free contact with this layer there is a third conducting wall, and a high. potential difi'erence is applied between the second wall and the first and third walls.

Our termination comprises a fiuidtight container, fiuidtight entrance means for a tapproof cable into the container and fiuidtight exit means for the cable core from the container. Although, in a preferred embodiment of our invention, this latter means is a sealed aperture in the container fitting the size of the core, the conductors comprising the core may be connected within the container to conductors of another cable ing film entirely covers this thickness, a second shield, which is metallic and is electrically connected to the second wall of each of the cables, covers the film and there is a second for which there is a fiuidtight exit in the container. These are cone, electrically connected to the second wall, is built up on the first layer; there is a stress-relief cone on the shielded cable and there are means for grounding the first and third walls and the shield of the shielded cable through the container. we prefer to have insulating oil surrounded the cables and stressrelief cones of our termination and substantially fill ourpontainer.

Our joint between a first and second tapproof cable comprises a plurality of connections between the conductors of the cables, which connections comprise a splice and a first conducting shield covering the splice and electrically connected to the first conducting wall of each of the cables. The second wall of each of the cables is stripped back to expose a length of the first layer of insulation and the third conducting wall of each cable is stripped back to expose-a length of the second insulating layer. Our joint also comprises a first continuous thickness of high-voltage insulation covering a length of the first layer of the-first cable, the splice, and a length of the first layer of the second cable. A first electrically conductthickness of high-voltage insulation'covering a length of the second layer of the'first cable, the second shield, and a length of the second layer of the second cable. A second electrically conducting film entirely covers the second thickness, and a third shield which is metallic and electrically connected to the third wall of each of the cables covers the film. Preferably, the thicknesses of high-voltage insulation are wrappings of insulating tape.

A more thorough understanding of our invention will be gained from the appended drawing:

In the drawing:

FIG. 1 is a side view of a termination made to our invention.

FIG. 2 is a side view of another embodiment of the termination of our invention.

FIGS. 30 and 3b combine to show a side view, in partial section, of a joint made to our invention.

FIG. 4 is a side view of an embodiment of a splice employing the termination of our invention.

In FIG. 1 a termination, indicated generally by the numeral 10, encloses the end of a tapproof cable 11 with a core 12 of insulated communication conductors l3, surrounded by an extruded jacket 14. The jacket 14 is covered by a first conducting wall 16 comprised of copper tapes embedded in an electrically conducting rubberlike compound, and this is insulated with a first layer of insulation 17, which is, in turn, covered by a second conducting wall 18. Although we have employed copper for the tapes of our conducting wall 16 it will be understood that other metals may be used within the scope of our invention. The wall 18 is insulated with a second insulating layer 19, covered with a third conducting wall 21 over which is applied a protective jacket 22. For the purposes of making a termination the various coverings comprising the cable 11 have been stepped back to expose the underlying elements. Thus the jacket 14 is cut off at a section 24 to expose the insulated communication conductors 13, the shielding wall 16 is cut off at a section 26, the insulating layer 17 is cut 011 at a section 27, the shielding wall 18 is cut off at a section 28, the insulating layer 19 is cut off at a section 29, the shielding wall 21 is cutoff at a section 31 and the jacket 11 is cut off at a section 32. The end of the cable 11 is enclosed in a tubular casing 33 which may be advantageously made of clear polymethylmethacrylate plastic, although metal casings may also be used for the casing 33 within the scope of our invention. The tube 33 has end plates 34, 36 fastened thereto by means of cup-shaped projections 37,38 and a suitable cement 35 or other fastening means of which many types are known. The plates 34,36 form part of end assemblies 39,41 respectively of a type described in Pat. application Ser. No. l50,7$5,

filed Nov. 7,. 1961 and assigned to the assignee of the present invention. The assemblies 39,41 include respective gaskets 42,43 and pressure plates 44,46, and it is a feature of these assemblies that when they are tightened by means of bolts 47 the material of the gaskets 42,43 extrudes inwardly to form a tight seal, such as seals 48,49 around the jackets 22 and 14, which pass through respective entrances 45,50 in the assemblies 39,41. By means of the gaskets 45, the end plates 34,36 are also sealed against the flange of the projections 37,38.

Starting at the section 28a stress-relief cone 51 is built up on the layer 17 by winding insulating tapes in a double taper in the known manner. Instead of wrapped tapes a preformed stress-relief cone may also be used'within the scope of our invention. The cone 51 is covered with a conducting surface 52 extending from the shield 18, with which it is in electrical contact, to a section 53 of maximum diameter of the cone 51. A similar stress-relief cone 54 is built up on the layer 19 extending from the section 31 and having a conducting surface 56. Surface 56 of the stress-relief cone 54 is grounded to the plate 34 by means of a grounding strap 57 and the shield 16 is grounded to the plate 36 by means of a groundingstrap 58. A shielded high-voltage cable 59 with a conductor 61 covered by a layer of insulation 62, a shielding wall 63, and overall jacket 64 is passedthrough an entrance 66 in the assembly 39 where it is sealed by an extruded seal-67. A stress-relief cone.68 is built up on the insulation 62 with a conducting surface 69 extendingfrom the shield 63 to a-maximum section 71. A conducting strap 72 connects the conductor 61 to the surface 52 thus serving to energize the conducting wall 18 to a high voltage such as 25 kv. A conducting strap 73 grounds the conducting surface 69 of the stress-relief cone 68 to the plate 34 and lugs 74,76 are provided to complete the grounding circuit by means of grounding conductors not shown. It will be understood that we do not wish to be limited to any particular form for the conducting straps 57,58 72,73 but they may advantageously be formed of braided copper or other metal wire. The high-voltage area of the termination is filled with an insulating oil 77 in such a manner that the air space forming above the oil is in an area at ground potential. Although we have illustrated the termination in a vertical position, it may be assembled horizontally, in which case it will be provided with oil filling vents such as those shown in FIG. 4 hereinafter to be described. The stress-relief cones 51, 54, 68 prevent corona discharges at the termination of the shielding walls which would result in spurious alarms being given at an ionization detector, not shown, which is connected between the conductor 61 and ground at some convenient point remote from the termination 10. An advantage of our termination that should be particularly noted is that the communication conductors 13, to which connections can be made, do not, at any point, pass through the high-voltage field created by the energized conductor 61, surface 52 or wall 18.

When one end of the cable 11 is terminated in the manner of FIG. 1 the other end may be terminated as shown in P16. 2. The termination of FIG. 2 differs from that of FIG. 1 in that no provision has been made for a high-voltage cable entrance to energize the wall 18 since current necessary for this purpose has been supplied at the other end of the cable by the shielded cable 59. A stress-relief cone 78 with a conducting surface 79 electrically connected to shield 18 is built up on the insulation 17 and a stress-relief cone 81 with a conducting surface 82 electrically connected to the shield 21 is built up on the insulating layer 19.

In FIGS. 3a and 3b we show a joint between two tapproof cables 11a and 11b. Such joints become necessary when very long cables are laid since there is a limit to the length of cable that can be manufactured and shipped and installed as a single, continuous unit. The joint, indicated generally by the numeral 100, differs from the termination 10 in having no oil filling and in being, itself, tapproof. Whereas the termination 10 must be located in a supervised location to prevent any unauthorized access to the conductors of the tapproof cable, joints, such as the joint 100, must be as tapproof as the cable itself, if the integrity of the installation is to be maintained. The joint 100 has a cylindrical casing 101 which may be polymethylmethacrylate resin or metal to protect it mechanically and the casing has end plate assemblies 102,103 similar to the plates used in the termination 10 and providing entrances 104,106 for the cables being joined. It will be understood that although the cable 110 in the left and 11b in the right-hand entrance of the casing 101 are identical, our invention also applies to embodiments where unlike cables are joined together, as may occur where a cable with a small number of conductors is spliced into a cable with a larger number. in the latter case provision may be made to bring more than two cable cores into the splice without exceeding the area of our discovery. If the cable is a buried cable the joint 100, being protected by the casing 101, can also be busplice there is applied an unbroken coating of conducting filrn 112, such as that described in U.S. Pat. No.-. 2,913,515, 'ex- Pat. No. 2,857,453. The tape 113 is wound to overlap the walls 16a and 16b and make electrical contact with the said walls. The tape 113 is covered in turn with wrappings of a conducting tape l14 that is soft enough to follow all the convolutions of the meshtape and to make intimate contact with the overlying insulation, hereafter to be described, at all points on its undersurface so that there will be no voids for possible corona discharges. A suitable soft tape is described in U.S. Pat. No. 3,049,584 assigned to Anaconda Wire and Cable Company as tape 3 in table 1 thereof. The splice 111 is considerably larger in diameter than the core of either of the" cables 11a or 11b and, being made by hand, has an irregular surface so that the conducting wall comprised of the film 112, mesh tape 113 and conducting tape 114 must be capable of covering a noncylindrical surface of double curvature. An insulating layer 17a of the cable 11a has been tapered off at a section 115 to expose the shield 16a, and a layer 17b of the ,cable 11b has been tapered off at a section 116 to expose the shield 16b, and conducting walls 18a, 18b have been cut at sections 117,118 to expose lengths 119,121 respectively of the insulations 17a and 17b. A continuous thickness of high-voltage insulation 122 is built up by wrapping insulating tape such as polyethylene insulating tape over the entire surface extending from the section 117 to the section 118 including insulation 119, exposed conducting wall 16a, conducting rubber tape 114, conducting wall 16b, and insulation 121.

The insulation 122 is coated with an unbroken coating of conducting film 124 which may be the same type of film used for the coating 112 in electrical contact with the walls 18a and 18b. Over this film there is wrapped an overlapped series of turns 126 of the conducting tape used for the turns 113. These turns overlap the walls 18a, 18b and are in electrical contact therewith. The conducting tape 126 is wrapped with a layer of conducting tape 127 of the same type as the tape 114. A third conducting wall 21a of the cable 110 is cut at a section 128 to expose a length 129 of a second insulating layer 19a with a taper 131 cut to expose the shield 18a and, complementarily, a third conducting wall 21b of the cable 11b is cut at a section 132 to expose a length 133 of a'second insulating layer 19b with a taper 134 cut to expose the shield 18b. A continuous thickness 136 of high-voltage insulation of. the same type as the thickness 122 is built up over the entire surface between the section 128 and the section 132. The insulation 136 is coated with a conducting film 137 of the same composition as the film 112 and then wrapped with a copper-mesh tape layer 138 which overlaps the conducting walls 21a and 21b. The mesh layer 138 may be covered with a wrap 139 of the soft conducting rubber used for the layer 114 although since the mesh layer and its outer surroundings are all at ground potential, this rubber layer is not an essential element of our joint. A

jacket 22a of the cable 1 la is cut off at a section 141 to expose Y the shield 21a and a jacket 22b is cut off at a section 142 to expose the shield 21b. A protective layer 143, which may advantageously be a carbon black filled polyethylene tape, but is not limited thereto, is wrapped over the entire joint surface from a section 144 of the jacket 22a to a section 146 of the jacket 22b. In our joint the second conducting wall comprising the film 124, mesh 126, and conducting-rubber tape 127 is maintained at high voltage since it is continuous with the energized cable walls and 18b. The conducting wall over it, comprised of the layers 137, 138, 1 39, and the conducting wall under it, comprised of the layers 112, 113, 114, are grounded since they are connected to the grounded walls of the cable. Any effort to penetrate the inner shield for the purpose of tapping the conductors will create a corona discharge Where it is not desired to make the joint tapproof as, for example, where it is situated in a guarded area, a joint such as that shown in FIGS. 4 may be used. Here each of the cables 1 10, 11b is terminated in the manner of FIG. 1 but a splice 147 between the conductors is included within a casing 148 that encloses both terminations. The insulating oil 77 serves also as insulation for the splice connections which are merely wrapped with an open mesh cotton tape 149 for mechanical protection. Oil vents 151,152 provided with screw caps 153,154 permit the casing to be completely filled with insulating oil which may be of a type, known for filling potheads, that solidifies upon cooling.

We have invented a new and useful cable termination and cable joint for which we desire an award of letters patent.

We claim:

1. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corrona-free contact therewith and having a high-potential difi'erenece applied between said second wall, and said first and third walls comprising:

A. a fluidtight container,

B. fluidtight entrance means for said tapproof cable into said container,

C. fluidtight exit means for said core from said container,

D. a shielded cable connecting said second wall within said container to a high-voltage source,

'5. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and

b. said second wall being stripped back to expose a length of said first layer,

F. a stress-relief cone, electrically connected to said third wall, built up on said second layer,

G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and

H. means grounding said first and third walls through said container.

2. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said core, a free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith,

' and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising:

A. a fluidtight container, 8. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. a shielded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer, F. a stress-relief cone, electrically connected to said third wall, built up on said second layer, G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, H. a stress-relief cone on said shielded cable within said container, and l. means grounding said first and third walls and the shield of said cable through said chamber.

3. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising:

A. a fluidtight container,

B. fluidtight entrance means for said tapproof cable into said container.

C. fluidtight exit means for said core from said container,

D. a shielded cable connecting said second wall within said container to a high-voltage source,

E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and i b. said second wall being stripped back to expose a length of said first layer,

F. a stress-relief cone, electrically connected to said third wall, built up on said second layer,

G. a stress-relief cone, electrically connected to said second wall, built up on said first layer,

H. insulating oil surrounding said cables and said cones and substantially filling said container, and

l. means grounding said first and third walls through said container.

4. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in coronafree contact therewith and having a high-potential difference applied between said second wall,

and said first and third walls, comprising:

A. a fluidtight container,

B. fluidtight entrance means for said tap-proof cable into said container,

C. fluidtight exit means for said core from said container,

D. a shielded cable connecting said second wall within said container to a high-voltage source,

E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer,

F. a stress-relief cone, electrically connected to said third wall, built up on said second layer,

G. a stress-relief cone, electrically connected to said second wall, built up on saidfirst layer,

H. a stress-relief cone on said shielded cable within said container,

1. insulating oil surrounding said cables and said cones and substantially filing said container, and

J. means grounding said first and third walls through said container.

5. A termination for a tapproof cable comprised of a core, a

first conducting wall surrounding said core, a first layer of in sulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising:

A. a fluidtight container,

B. fiuidtight entrance means for said tapproof cable into said container,

C. fiuidtight exit means for said core from said container,

D. a shielded cable connecting said second wall within said container to a high-voltage source,

E. fiuidtight entrance means for said shielded cable into said container,

F. insulating oil surrounding said cables and substantially filling said container, and

G. means grounding said first and third walls through said container.

6. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact threwith, a second conducting wall surrounding said layer in coronafree contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difi'erence applied between said second wall, and said first and third walls comprising:

A. a fluidtight container,

B. fluidtight entrance means for said tapproof cable into said container,

C. fluidtight exit means for said core from said container,

D. within said container said third wall being stripped back to expose a length of said second layer and said second wall being stripped back to expose a length of said first layer,

E. a stress-relief cone, electrically connected to said third wall, built up on said second layer,

F. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and

6. means grounding said first and third walls through said container.

7. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in' corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising:

v A. a fluidtight container,

B. fluidtight entrance means for said tapproof cable into said container,

C. fluidtight exit means for said core from said container,

D. within said container said third wall being stripped back to expose a lengthof said second layer and said second wall being stripped back to expose a length of said first layer,

E. a stress-relief cone, electrically connected to said third wall, built up on said second layer,

F. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and

insulating oil surrounding said cables and said cones and substantially filling said container, and

H. means grounding said first and third walls through said container.

8. A tapproof joint between a first and a second tapproofcable, each comprised of a plurality of conductors forming a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall,

and said first and third walls comprising: A. a plurality of connections between the conductors of said cables com rising a cable splice,

B. a first con ucting shield covering said splice,

a. said shield being electrically connected to said first wall of each of said cables,

b. said second wall of each of said cables being stripped back to expose a length of said first layer, and

c. said third wall of each of said cables being stripped back to expose a length of said second layer,

C. a first continuous thickness of high-voltage insulation covering, in corona-free contact therewith, a length of said first layer of said first cable, said splice, and, in corona-free contact therewith, a length of said first layer of said second cable,

D. a second conducting shield intimately covering said first thickness,

a. said second shield being electrically connected to sai second wall of each of said cables, I

E. a second continuous thickness of high-voltage insulation covering, in corona-free contact therewith, a length of said second layer of said first cable, said second shield, and, in corona-free contact therewith, a length of said second layer of said second cable,

F. a third conducting shield intimately covering, in coronafree contact therewith, said second thickness, and a. being electrically connected to said third wall of each of said cables.

9. The joint of claim 8 wherein said thicknesses are wrappings of insulating tape.

10. A tapproof joint between a first and second tapproof cable, each comprised of a plurality of conductors forming a core, a firstconducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third'conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall,

' and said first and third walls comprising:

A. a plurality of connections between the conductors of said cables comprising a cable splice,

B. a first conducting shield covering said splice,

a. said shield being electrically connected to said first wall of each of said cables,

b. said second wall of each of said cables being stripped back to expose a length of said first layer, and

c. said third wall of each of said cables being stripped back to expose a length of said second layer,

C. a first continuous thickness of high-voltage insulation covering a length of said first layer of said first cable, said splice, and a length of said first layer of said second cable,

D. a first electrically conducting film entirely covering said first thickness,

E. a second shield covering said first film a. said second shield being metallic and b. electrically connected to said second wall of each of said cables,

' F. a second continuous thickness of high-voltage insulation covering a length of said second layer of said first cable, said second shield, and a length of said second layer of said second cable,

G. a second electrically conducting film entirely covering said second thickness,

H. a third shield covering said second film a. said third shield being metallic and b. electrically connected to said third wall of each of said cables.

11. The joint of claim 10 wherein said thicknesses are wrappings of insulating tape. 

1. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corrona-free contact therewith and having a highpotential differenece applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. a shiElded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer, F. a stress-relief cone, electrically connected to said third wall, built up on said second layer, G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and H. means grounding said first and third walls through said container.
 2. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said core, a free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. a shielded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer, F. a stress-relief cone, electrically connected to said third wall, built up on said second layer, G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, H. a stress-relief cone on said shielded cable within said container, and I. means grounding said first and third walls and the shield of said cable through said chamber.
 3. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container. C. fluidtight exit means for said core from said container, D. a shielded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer, F. a stress-relief cone, electrically connected to said third wall, built up on said second layer, G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, H. insulating oil surrounding said cables and said cones and substantially filling said container, and I. means grounding said first and third walls through said container.
 4. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrOunding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls, comprising: A. a fluidtight container, B. fluidtight entrance means for said tap-proof cable into said container, C. fluidtight exit means for said core from said container, D. a shielded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, within said container a. said third wall being stripped back to expose a length of said second layer, and b. said second wall being stripped back to expose a length of said first layer, F. a stress-relief cone, electrically connected to said third wall, built up on said second layer, G. a stress-relief cone, electrically connected to said second wall, built up on said first layer, H. a stress-relief cone on said shielded cable within said container, I. insulating oil surrounding said cables and said cones and substantially filing said container, and J. means grounding said first and third walls through said container.
 5. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. a shielded cable connecting said second wall within said container to a high-voltage source, E. fluidtight entrance means for said shielded cable into said container, F. insulating oil surrounding said cables and substantially filling said container, and G. means grounding said first and third walls through said container.
 6. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact threwith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. within said container said third wall being stripped back to expose a length of said second layer and said second wall being stripped back to expose a length of said first layer, E. a stress-relief cone, electrically connected to said third wall, built up on said second layer, F. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and G. means grounding said first and third walls through said container.
 7. A termination for a tapproof cable comprised of a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-fRee contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a fluidtight container, B. fluidtight entrance means for said tapproof cable into said container, C. fluidtight exit means for said core from said container, D. within said container said third wall being stripped back to expose a length of said second layer and said second wall being stripped back to expose a length of said first layer, E. a stress-relief cone, electrically connected to said third wall, built up on said second layer, F. a stress-relief cone, electrically connected to said second wall, built up on said first layer, and insulating oil surrounding said cables and said cones and substantially filling said container, and H. means grounding said first and third walls through said container.
 8. A tapproof joint between a first and a second tapproof cable, each comprised of a plurality of conductors forming a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a plurality of connections between the conductors of said cables comprising a cable splice, B. a first conducting shield covering said splice, a. said shield being electrically connected to said first wall of each of said cables, b. said second wall of each of said cables being stripped back to expose a length of said first layer, and c. said third wall of each of said cables being stripped back to expose a length of said second layer, C. a first continuous thickness of high-voltage insulation covering, in corona-free contact therewith, a length of said first layer of said first cable, said splice, and, in corona-free contact therewith, a length of said first layer of said second cable, D. a second conducting shield intimately covering said first thickness, a. said second shield being electrically connected to said second wall of each of said cables, E. a second continuous thickness of high-voltage insulation covering, in corona-free contact therewith, a length of said second layer of said first cable, said second shield, and, in corona-free contact therewith, a length of said second layer of said second cable, F. a third conducting shield intimately covering, in corona-free contact therewith, said second thickness, and a. being electrically connected to said third wall of each of said cables.
 9. The joint of claim 8 wherein said thicknesses are wrappings of insulating tape.
 10. A tapproof joint between a first and second tapproof cable, each comprised of a plurality of conductors forming a core, a first conducting wall surrounding said core, a first layer of insulation surrounding said wall in corona-free contact therewith, a second conducting wall surrounding said layer in corona-free contact therewith, a second layer of insulation surrounding said second conducting wall in corona-free contact therewith, and a third conducting wall surrounding said second layer in corona-free contact therewith and having a high-potential difference applied between said second wall, and said first and third walls comprising: A. a plurality of connections between the conductors of said cables comprising a cable splice, B. a first conducting shield covering said splice, a. said shield being electrically connected to said first wall of each of said cables, b. said second wall oF each of said cables being stripped back to expose a length of said first layer, and c. said third wall of each of said cables being stripped back to expose a length of said second layer, C. a first continuous thickness of high-voltage insulation covering a length of said first layer of said first cable, said splice, and a length of said first layer of said second cable, D. a first electrically conducting film entirely covering said first thickness, E. a second shield covering said first film a. said second shield being metallic and b. electrically connected to said second wall of each of said cables, F. a second continuous thickness of high-voltage insulation covering a length of said second layer of said first cable, said second shield, and a length of said second layer of said second cable, G. a second electrically conducting film entirely covering said second thickness, H. a third shield covering said second film a. said third shield being metallic and b. electrically connected to said third wall of each of said cables.
 11. The joint of claim 10 wherein said thicknesses are wrappings of insulating tape. 